Frequency control system



Nov. 12, 1946.

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FREQUENCY 0-0 STABILIZED OSCILLATOR Patented Nov. 12, 1946 FREQUENCY CONTROL SYSTEM Edward L. Ginzton, Wantagh, Winslow Palmer,

West Hempstead, and Frederic A. Jenks, Rockville Centre, N. Y., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application May 19, 1942, Serial No. 443,605

15 Claims. (01. 25o -36) This invention relates, generally, to automatic frequency control, and, the invention has reference, more specifically, to a type of automatic frequency control system most useful for controlling the output frequency of ultra high frequency oscillators'of the electron beam velocity modulation type.

I prior art frequency control systems operating at radio frequencies, it has been common to use a thermostatically controlled quartz-crystal oscillator and to obtain higher frequencies there'- from by the use of conventional vacuum tube frequency multiplication circuits. At radio or intermediate frequencies, multiplier tubes having sufiicient output to drive'the succeeding multiplication stage are well known to the art, but at the ultra high frequencies at which electron beam velocity modulation tubes of the type disclosed in prior United States Patent Number 2,242,275 entitled, Electrical translating device, filed October 11, 1937, in the name of Russell H. Varian, operate, it is diflicult to provide sufiicient driving voltage to give optimum excitation of the first resonator of the electron beam velocity modulation tube acting as the last step in the multiplication chain. Without such an excitation level, further steps of amplification at ultra high frequency would be required, thus necessitating control devices for tuning many resonators, probably individually, to the operating frequency.

It is, therefore, one object of the present invention to provide an automatic sensitive frequency control system especially adapted to the control of the output frequency of radio apparatus such as high power ultra-high frequency electron beam velocity modulation oscillators, the said system being operable even under conditions of large deviation from the desired output frequency.

An object of the invention is to provide an automatic frequency control system in which operation of the control system is relatively uninfiuenced by the loading of the equipment controlled.

A further object is to provide an automatic frequency control system utilizing broad and narrow band discriminators adapted to control radio equipment such as electron beam velocity modulation oscillators or of other types of oscillators over a large range to correct the effects of varying operating parameters such as temperature changes.

An object of the present invention lies in the provision of an automatic frequency control system for control of a high power electron beam velocity modulation oscillator, utilizing as a. reference frequency a low-power electron beam velocity modulation multiplier tube whose frequency output i stabilized as by means of a quartzcrystal oscillator used in connection with a conventional vacuum tube frequency multiplication circuit.

A further object lies in the provision of an automatic frequency control system utilizing the parent from specifications taken in connection 1 with the accompanying drawing, wherein the in vention is embodied in concrete form.

In the drawing,

Fig. 1 is a schematic wiring diagram of the preferred form of the present invention.

Fig. 2 is an explanatory graph.

Fig. 3 is an alternate form of a portion of Fig. 1.

Referring now to Fig. 1, there is shown at l a conventional three resonator electron beam velocity modulation tube, such as has been previously disclosed in copending application Serial Number 393,868, entitled High frequency tube structure, filed May 1'7, 1941, in the names of William W. Hansen and John R. Woodyard. The first two resonators of the device are coupled by the coaxial line 2, these two resonators serving in the conventional manner as an ultra high frequency oscillator. Resonators I and 5 are electrically coupled only by the electron beam from the cathode, and resonator 5 serves in a well known manner as a buffer resonator so that loading of resonator 5 does not afiect the output frequency of the oscillator. Ultra high frequency energy may be extracted from resonator 5 by means of coaxial line 6, which may lead to any desired type of utilization apparatus. Inserted into the walls of resonators 3 and 4 are shown metal or dielectric plugs 'l and 8, which may be inserted to a greater or lesser degree into resonators 3 and 4 by rotation of gearing 9 and Ill by shaft H. The tuning plugs-1 and 8 distort the electro-magnetic field inside of the resonators 3 and 4, thus altering the natural frequency of these resonators, as described in United States Patent Number 2,259,690, entitled High frequency radio apparatus, filed April 20, 1939, in the names of John R. Woodyard, William W. Hansen, and Russell H. Varian. Any other well known type of. mechanical or electrical tuning device may be used in connection with resonators 3, 4,

3 and, resonator I may be also tuned, if desired, although resonator 3 need not be, as it is not a frequency determining element.

By means of coupling loop l2 inserted in res- .onator 4, an arbitrary portion of the ultra high frequency energy therein is introduced through coaxial line l3 to ultra high frequency mixer i4. This frequency f1 may be, for instance, 3000 megacycles per second.

A conventional frequency stabilized oscillator II, which may be of the quartz-crystal variety, supplies a frequency f to a conventional vacuum tube frequency multiplier circuit ii. If the frequency multiplication constant of multiplier I6 is n, this output frequency of multiplier l6 supplied through coaxial line I! to resonator ll of electron beam velocity modulation multiplier tube i3, is then nf. Oscillator l5 and multipliers l6 and I3 constitute a stabilized frequency multiplication chain. The operation of the multiplier I! has been shown in copending application Serial Number 416,170, entitled A high frequency electron tube structure, filed October 23, 1941, by William W. Hansen, John R. Woodyard, Sigurd F. Varian, and Russell H. Varian, to be that of utilization of harmonic components of the velocity modulated electron beam to produce harmonics of the frequency producing the velocity modulation. The multiplication constant of multiplier I9 is chosen so that the output frequency of resonator 2|, supplied through coaxial line 20 to mixer I4, is very close to frequency 11. For instance, if this freq'ien'y ,f: is made 2975 megacycles per second, the output of mixer i4 is then 11-h or 25 megacycles per second in the example given.

This output frequency may be further amplifled by intermediate frequency amplifier 22 and supplied to a broad band frequency discriminator 23, whose reversing polarity direct current output is shown as a function of frequency at 24 in Fig. 2. A portion of the frequency ,fi-j: is supplied by means of lead 25 to an intermediate frequency mixer 26. Also supplied to mixer 26 is a frequency 11! derived at any convenient point in frequency multiplier i6. Frequency nf is preferably made very close in frequency to the value of ji-h. For instance, if .fi-fa is made 25 megacycles, frequency 11f may conveniently be 30 megacycles. The output frequency of mixer 26 is fed to intermediate frequency amplifier 21, and from there to a narrow band discriminator 28. The reversing polarity direct current output of discriminator 23 ha the frequency characteristic shown at 23 in Fig. 2. At 30 in Fig. 2 is shown the combined output of the discriminators 23 and 26, which appears on leads 3| and 32 to be supplied to direct current amplifier 33. The output of direct current amplifier 33- may be conveniently supplied to the field coils 34 and 35 of a direct current motor 36, whose armature 31, is supplied from a source of constant voltage, such as by battery 38. It is seen that the pass bands of discriminators 23, 28, may have any convenient value.

It is seen that the provision of the desired frequencies for use in the discriminators 23, 28 can be obtained in many ways. For instance, if desired, a third frequency U can be derived from the frequency multiplier ii to be mixed with the output of intermediate frequency amplifier 21, and, after further amplification, to be applied to a very narrow band discriminator in place of discriminator 28. It is seen that the system shown in Fig. 1 provides an auto atic frequency control system using a broad band discriminator to drive the tuning device under conditions of large deviation from the desired output frequency, and a-narrow band discriminator to provide very tight and positive control about the desired frequency. A further advantage of the use of two channels is that the narrow band discriminator provides a much greater absolute stability of the controlling output about the chosen frequency than would a single broad band discriminator of equal tightness.

In Fig. 3, there is shown a modification of a portion of the system of Fig. 1 which may be used to replace direct current amplifier 33 and motor 36 and which will afford improved operation of the system. The apparatus and circuit shown in Fig. 3 is substitutable bodily in place of that shown in the dot-dash line rectangle in Fig. 1, the connections to tuning shaft II and leads 3| and 32 being clearly indicated. Here the reversing polarity direct current signal appearing on leads 3|, 32 is applied to a voltage amplifier 39, the output of which is converted by balanced modulator 40 to a variable magnitude phase reversing alternating voltage, balanced modulator 40 being supplied by any convenient source of alternating current placed on leads 49. The output of balanced modulator 40 is supplied to conventional power amplifier 4|, whose output is, in turn, applied to one coil of two phase induction motor 44, the other coil of which is supplied from the same alternating current source as is balanced modulator 40.

If desired, an anticipation signal may be applied to the amplifier input 33 by use of a conventional field distortion generator 45, rotated by extension 50 of shaft II, which is in turn attached to motor 44 to drive tuning plugs 8 and ID. The same source of alternating current as applied to coil 43 and to modulator 40 is applied to one coil, 41, of the field distortion generator 45. The output of the other coil, 45, is then proportional to the rate of rotation of shaft 50, and may be applied in any convenient manner to the input of amplifier 33, introducing a signal to the system which causes the motor to apply a torque proportional to and opposing its own motion, thus providing damping and smoothing of the operation of the system.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A stabilization system for stabilizing the frequency of an oscillator comprising, supply means for producing a reference voltage of a frequency somewhat different from the desired frequency of operation of said oscillator, a mixer connected for receiving energy from said oscillater and from said supply means, a broad band discriminator connected for receiving a version of the output of said mixer, a second mixer connected for receiving a portion of the output of said first mixer and for receiving a second reference voltage from said supply means, such second reference voltage being of a frequency close to that of the output of said first mixer, a narrow band pass discriminator connected for receiving a version of the output of said second mixer, means for connecting the outputs of said means.

2. In apparatus of the character described, an

ultra high frequency high power oscillator, motive means for tuning said oscillator, a stabilized frequency multiplication chain, a mixer connected for receiving energy from said multiplication chain and from said power oscillator, a broad band discriminator supplied from said mixer, a second mixer supplied from said first mixer and from said multiplication chain, a narrow band discriminator supplied from said second mixer, and means connecting the outputs of said discriminators in series and connected for controlling said tuning motive means.

3. Means for stabilizing the operating frequency of an ultra high frequency power oscillator comprising, tuning motive means connected for tuning said power oscillator, a stabilized frequency multiplication chain, a mixer connected to be supplied with a portion of the output of said power oscillator and with a voltage from said multiplication chain of a frequency near that of said oscillator, means for amplifying the difference output of said mixer, a broad band discriminator connected to be fed from said amplifier, a second mixer connected for receiving a portion of the output of said amplifier and for receiving a voltage from said stabilized frequency multiplication chain of a frequency near that of the output of said amplifier, an amplifier connected for amplifying the output of said second mixer, a narrow band discriminator fed from said last named amplifier, and means connected for receiving the outputs of said discriminators and for controlling said tuning motive means in accordance with the sum thereof.

4. Apparatus as defined in claim' 3 wherein said means for receiving the outputs of said discriminators comprises a balanced modulator for converting the resultant direct current output of said discriminators to a variable magnitude, reversible phase alternating voltage for controlling said tuning motive means. I

5. Apparatus of the character described for stabilizing the frequency of a power oscillator having tuning motive means, comprising a stabilized frequency multiplication chain, a mixer connected for receiving a voltage from said chain and from said power oscillator to produce a difference frequency voltage, a broad band discriminator connected to be fed with a version of said difference frequency voltage, a second mixer also connected to be fed with a version of said difference frequency voltage and with a voltage from said frequency multiplication chain of a somewhat different frequency, a narrow band discriminator fed with a version of the output of said second mixer, means for connecting the outputs of said discriminators in series, means for amplifying said combined discriminator outputs, balanced modulator means for converting said outputs to a reversible-phase signal for controlling said tuning motive means, and generator means responsive to the velocity of said tuning motive means for supplying a negative feed back to said balanced modulator to prevent hunting of said tuning motive means.

6. In a system for automatically controlling the output frequency of a source, means providing a signal of reference frequency, means for mixing voltages from said source and said signal providing means for deriving a first frequency different from said source frequency and varying in synchronism therewith, means coupled to said source and said signal-providing means for deriving a second frequency of a diiferent order of magnitude from said first frequency and also varying in synchronism with said source frequency, broad and narrow band discriminators coupled to said mixing means and said second frequency-deriving means and responsive respectively to the greater and lesser of said first and second frequencies for producing respective output signals corresponding to deviations of said first and second frequencies from respective predetermined values, variable means for controlling the frequency of said source, and means responsive to the outputs of said discriminators for controlling said variable means.

7. In a system for automatically controlling frequency, a source, means providing a signal of reference frequency, means for mixing voltages from said source and said signal-providing means to produce a. difference frequency, broad and narrow band discriminators connected to said mixing means and responsive to said difference frequency to produce respective output signals corresponding to deviation of said difference frequency from a desired value, said broad-band discriminator beingresponsive to deviations extending over a relatively large range, and said narrow-band discriminator being responsive only to deviations over a relatively small range, variable means for controlling the frequency of said source, means for connecting said signals in series and means responsive to said series connected signals for operating said variable means.

8. In a system for automatically controlling the output frequency of a source, stabilized frequency supply means, a first frequency multiplier connected to said supply means, a second frequency multiplier connected to the output of said first frequency multiplier, means for mixing the outputs of said source and said second frequency multiplier, means for mixing the outputs of said first frequency multiplier and said first mixing means, variable means for controlling the frequency of said source, and frequency sensitive means responsive to the outputs of said mixing means for controlling said variable means, said frequency-sensitive means comprising a broadband discriminator connected to said first mixing means, a narrow-band discriminator connected to said second mixing means, and means combining the outputs of said discriminators.

9. In apparatus for stabilizing the operating frequency of an oscillator, variable means for tuning said oscillator, a stabilized frequency multiplication chain, a mixer connected to be supplied with a portion of the output of said oscillator and with a voltage from said multiplication chain of a frequency near that of the oscillator, a broad band discriminator connected to said mixer, a. second mixer connected for receiving a portion of the output of said first mixer and for receiving a voltage from said frequency multiplication chain of a frequency near the output frequency of said first mixer, a narrow band discriminator connected to said second mixer, and means connected for combining the outputs of said discriminators and for controlling said variable tuning means in accord therewith.

10. The apparatus defined in claim 9, wherein said means for combining the outputs of said discriminators comprises means for converting the direct current output of said discriminators 7 to a variable magnitude and reversible phase alternating voltage for controlling said variable tuning means.

11. Automatic frequency stabilization apparatus comprising an oscillator, the output frequency of which is to be stabilized, variable means for tuning said oscillator, means providing a reference frequency, frequency sensitive moans connected to said oscillator and to said reference frequency means, said frequency sensitive means embodying means operable to produce an output signal representing the amount of deviation of said oscillator frequency from a desired relation with respect to said reference frequency and over a relatively large range of such deviation, and also embodying further means operable to produce a second output signal representing the amount of said deviation over only a relatively small range of such deviation, said second signal being greater than said first signal for equal deviations within said small range, means combining said signals in series, and means for connecting the output of said combining means to said variable tuning means to actuate said tuning means.

12. In a system for automatically controlling frequency, an oscillator, stabilized frequency supply means, frequency multiplier means connected to said supply means, a mixer inter-connecting said multiplier means and said oscillator to produce a first difference frequency, a second mixer coupled to the outputs of said first mixerand narrow band discriminators connected to said mixers and responsive respectively to deviations of said first and second diflerence frequencies from respective predetermined values, said narrow-band discriminator being adapted to produce a greater oscillator tuning effect for a small change in said second difference frequency than said broad-band discriminator.

14. In a system for automatically controlling frequency, a source of frequency to be controlled, stabilized frequency supply means, a mixer, means for introducing a voltage from said source into said mixer, means for introducing into said mixer a voltage of a frequency which is a version of said supply frequency, a second mixer, means for introducing into said second mixer a voltage of a frequency which is another version of said supply frequency, means introducing a version of the output of said first mixer into said second mixer, variable means controlling the frequency of said source, and frequency sensitive means responsive to the outputs of said mixers for controlling said variable means, said frequency sensitive means comprising a broad-band discriminator coupled to said first mixer and a narrow-band discriminator coupled to said second mixer.

15. High frequency apparatus comprising an ultra high frequency oscillator, means for tuning said oscillator, a source of reference frequency, a mixer connected for receiving energy from said reference frequency source and from said oscillator, a broad-band discriminator supplied from said mixer, a source of second -reference frequency, a second mixer supplied from said first mixer and from said second source, a narrowband discriminator supplied from said second mixer, and means responsive to the outputs of said discriminators for controlling said tuning motive means.

EDWARD L. GINZTON. WINSLOW PALMER. FREDERIC A. JENKS. 

